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<head><title>HTTP/1.1: Method Definitions
</title></head>
<body><address><p>part of <a rev='Section' href='rfc2616.html'>Hypertext Transfer Protocol -- HTTP/1.1</a><br />
RFC 2616 Fielding, et al.</p></address>
<h2><a name='sec9'>9</a> Method Definitions
</h2>
<p>
   The set of common methods for HTTP/1.1 is defined below. Although
   this set can be expanded, additional methods cannot be assumed to
   share the same semantics for separately extended clients and servers.
</p>
<p>
   The Host request-header field (section <a rel='xref' href='rfc2616-sec14.html#sec14.23'>14.23</a>) MUST accompany all
   HTTP/1.1 requests.
</p>
<h3><a name='sec9.1'>9.1</a> Safe and Idempotent Methods
</h3>
<h3><a name='sec9.1.1'>9.1.1</a> Safe Methods
</h3>
<p>
   Implementors should be aware that the software represents the user in
   their interactions over the Internet, and should be careful to allow
   the user to be aware of any actions they might take which may have an
   unexpected significance to themselves or others.
</p>
<p>
   In particular, the convention has been established that the GET and
   HEAD methods SHOULD NOT have the significance of taking an action
   other than retrieval. These methods ought to be considered "safe".
   This allows user agents to represent other methods, such as POST, PUT
   and DELETE, in a special way, so that the user is made aware of the
   fact that a possibly unsafe action is being requested.
</p>
<p>
   Naturally, it is not possible to ensure that the server does not
   generate side-effects as a result of performing a GET request; in
   fact, some dynamic resources consider that a feature. The important
   distinction here is that the user did not request the side-effects,
   so therefore cannot be held accountable for them.
</p>
<h3><a name='sec9.1.2'>9.1.2</a> Idempotent Methods
</h3>
<p>
   Methods can also have the property of "idempotence" in that (aside
   from error or expiration issues) the side-effects of N > 0 identical
   requests is the same as for a single request. The methods GET, HEAD,
   PUT and DELETE share this property. Also, the methods OPTIONS and
   TRACE SHOULD NOT have side effects, and so are inherently idempotent.
</p>
<p>
   However, it is possible that a sequence of several requests is non-
   idempotent, even if all of the methods executed in that sequence are
   idempotent. (A sequence is idempotent if a single execution of the
   entire sequence always yields a result that is not changed by a
   reexecution of all, or part, of that sequence.) For example, a
   sequence is non-idempotent if its result depends on a value that is
   later modified in the same sequence.
</p>
<p>
   A sequence that never has side effects is idempotent, by definition
   (provided that no concurrent operations are being executed on the
   same set of resources).
</p>
<h3><a name='sec9.2'>9.2</a> OPTIONS
</h3>
<p>
   The OPTIONS method represents a request for information about the
   communication options available on the request/response chain
   identified by the Request-URI. This method allows the client to
   determine the options and/or requirements associated with a resource,
   or the capabilities of a server, without implying a resource action
   or initiating a resource retrieval.
</p>
<p>
   Responses to this method are not cacheable.
</p>
<p>
   If the OPTIONS request includes an entity-body (as indicated by the
   presence of Content-Length or Transfer-Encoding), then the media type
   MUST be indicated by a Content-Type field. Although this
   specification does not define any use for such a body, future
   extensions to HTTP might use the OPTIONS body to make more detailed
   queries on the server. A server that does not support such an
   extension MAY discard the request body.
</p>
<p>
   If the Request-URI is an asterisk ("*"), the OPTIONS request is
   intended to apply to the server in general rather than to a specific
   resource. Since a server's communication options typically depend on
   the resource, the "*" request is only useful as a "ping" or "no-op"
   type of method; it does nothing beyond allowing the client to test
   the capabilities of the server. For example, this can be used to test
   a proxy for HTTP/1.1 compliance (or lack thereof).
</p>
<p>
   If the Request-URI is not an asterisk, the OPTIONS request applies
   only to the options that are available when communicating with that
   resource.
</p>
<p>
   A 200 response SHOULD include any header fields that indicate
   optional features implemented by the server and applicable to that
   resource (e.g., Allow), possibly including extensions not defined by
   this specification. The response body, if any, SHOULD also include
   information about the communication options. The format for such a
</p>
<p>
   body is not defined by this specification, but might be defined by
   future extensions to HTTP. Content negotiation MAY be used to select
   the appropriate response format. If no response body is included, the
   response MUST include a Content-Length field with a field-value of
   "0".
</p>
<p>
   The Max-Forwards request-header field MAY be used to target a
   specific proxy in the request chain. When a proxy receives an OPTIONS
   request on an absoluteURI for which request forwarding is permitted,
   the proxy MUST check for a Max-Forwards field. If the Max-Forwards
   field-value is zero ("0"), the proxy MUST NOT forward the message;
   instead, the proxy SHOULD respond with its own communication options.
   If the Max-Forwards field-value is an integer greater than zero, the
   proxy MUST decrement the field-value when it forwards the request. If
   no Max-Forwards field is present in the request, then the forwarded
   request MUST NOT include a Max-Forwards field.
</p>
<h3><a name='sec9.3'>9.3</a> GET
</h3>
<p>
   The GET method means retrieve whatever information (in the form of an
   entity) is identified by the Request-URI. If the Request-URI refers
   to a data-producing process, it is the produced data which shall be
   returned as the entity in the response and not the source text of the
   process, unless that text happens to be the output of the process.
</p>
<p>
   The semantics of the GET method change to a "conditional GET" if the
   request message includes an If-Modified-Since, If-Unmodified-Since,
   If-Match, If-None-Match, or If-Range header field. A conditional GET
   method requests that the entity be transferred only under the
   circumstances described by the conditional header field(s). The
   conditional GET method is intended to reduce unnecessary network
   usage by allowing cached entities to be refreshed without requiring
   multiple requests or transferring data already held by the client.
</p>
<p>
   The semantics of the GET method change to a "partial GET" if the
   request message includes a Range header field. A partial GET requests
   that only part of the entity be transferred, as described in section
   <a rel='xref' href='rfc2616-sec14.html#sec14.35'>14.35</a>. The partial GET method is intended to reduce unnecessary
   network usage by allowing partially-retrieved entities to be
   completed without transferring data already held by the client.
</p>
<p>
   The response to a GET request is cacheable if and only if it meets
   the requirements for HTTP caching described in section 13.
</p>
<p>
   See section <a rel='xref' href='rfc2616-sec15.html#sec15.1.3'>15.1.3</a> for security considerations when used for forms.
</p>
<h3><a name='sec9.4'>9.4</a> HEAD
</h3>
<p>
   The HEAD method is identical to GET except that the server MUST NOT
   return a message-body in the response. The metainformation contained
   in the HTTP headers in response to a HEAD request SHOULD be identical
   to the information sent in response to a GET request. This method can
   be used for obtaining metainformation about the entity implied by the
   request without transferring the entity-body itself. This method is
   often used for testing hypertext links for validity, accessibility,
   and recent modification.
</p>
<p>
   The response to a HEAD request MAY be cacheable in the sense that the
   information contained in the response MAY be used to update a
   previously cached entity from that resource. If the new field values
   indicate that the cached entity differs from the current entity (as
   would be indicated by a change in Content-Length, Content-MD5, ETag
   or Last-Modified), then the cache MUST treat the cache entry as
   stale.
</p>
<h3><a name='sec9.5'>9.5</a> POST
</h3>
<p>
   The POST method is used to request that the origin server accept the
   entity enclosed in the request as a new subordinate of the resource
   identified by the Request-URI in the Request-Line. POST is designed
   to allow a uniform method to cover the following functions:
</p>
<pre>      - Annotation of existing resources;
</pre>
<pre>      - Posting a message to a bulletin board, newsgroup, mailing list,
        or similar group of articles;
</pre>
<pre>      - Providing a block of data, such as the result of submitting a
        form, to a data-handling process;
</pre>
<pre>      - Extending a database through an append operation.
</pre>
<p>
   The actual function performed by the POST method is determined by the
   server and is usually dependent on the Request-URI. The posted entity
   is subordinate to that URI in the same way that a file is subordinate
   to a directory containing it, a news article is subordinate to a
   newsgroup to which it is posted, or a record is subordinate to a
   database.
</p>
<p>
   The action performed by the POST method might not result in a
   resource that can be identified by a URI. In this case, either 200
   (OK) or 204 (No Content) is the appropriate response status,
   depending on whether or not the response includes an entity that
   describes the result.
</p>
<p>
   If a resource has been created on the origin server, the response
   SHOULD be 201 (Created) and contain an entity which describes the
   status of the request and refers to the new resource, and a Location
   header (see section <a rel='xref' href='rfc2616-sec14.html#sec14.30'>14.30</a>).
</p>
<p>
   Responses to this method are not cacheable, unless the response
   includes appropriate Cache-Control or Expires header fields. However,
   the 303 (See Other) response can be used to direct the user agent to
   retrieve a cacheable resource.
</p>
<p>
   POST requests MUST obey the message transmission requirements set out
   in section 8.2.
</p>
<p>
   See section <a rel='xref' href='rfc2616-sec15.html#sec15.1.3'>15.1.3</a> for security considerations.
</p>
<h3><a name='sec9.6'>9.6</a> PUT
</h3>
<p>
   The PUT method requests that the enclosed entity be stored under the
   supplied Request-URI. If the Request-URI refers to an already
   existing resource, the enclosed entity SHOULD be considered as a
   modified version of the one residing on the origin server. If the
   Request-URI does not point to an existing resource, and that URI is
   capable of being defined as a new resource by the requesting user
   agent, the origin server can create the resource with that URI. If a
   new resource is created, the origin server MUST inform the user agent
   via the 201 (Created) response. If an existing resource is modified,
   either the 200 (OK) or 204 (No Content) response codes SHOULD be sent
   to indicate successful completion of the request. If the resource
   could not be created or modified with the Request-URI, an appropriate
   error response SHOULD be given that reflects the nature of the
   problem. The recipient of the entity MUST NOT ignore any Content-*
   (e.g. Content-Range) headers that it does not understand or implement
   and MUST return a 501 (Not Implemented) response in such cases.
</p>
<p>
   If the request passes through a cache and the Request-URI identifies
   one or more currently cached entities, those entries SHOULD be
   treated as stale. Responses to this method are not cacheable.
</p>
<p>
   The fundamental difference between the POST and PUT requests is
   reflected in the different meaning of the Request-URI. The URI in a
   POST request identifies the resource that will handle the enclosed
   entity. That resource might be a data-accepting process, a gateway to
   some other protocol, or a separate entity that accepts annotations.
   In contrast, the URI in a PUT request identifies the entity enclosed
   with the request -- the user agent knows what URI is intended and the
   server MUST NOT attempt to apply the request to some other resource.
   If the server desires that the request be applied to a different URI,
</p>
<p>
   it MUST send a 301 (Moved Permanently) response; the user agent MAY
   then make its own decision regarding whether or not to redirect the
   request.
</p>
<p>
   A single resource MAY be identified by many different URIs. For
   example, an article might have a URI for identifying "the current
   version" which is separate from the URI identifying each particular
   version. In this case, a PUT request on a general URI might result in
   several other URIs being defined by the origin server.
</p>
<p>
   HTTP/1.1 does not define how a PUT method affects the state of an
   origin server.
</p>
<p>
   PUT requests MUST obey the message transmission requirements set out
   in section 8.2.
</p>
<p>
   Unless otherwise specified for a particular entity-header, the
   entity-headers in the PUT request SHOULD be applied to the resource
   created or modified by the PUT.
</p>
<h3><a name='sec9.7'>9.7</a> DELETE
</h3>
<p>
   The DELETE method requests that the origin server delete the resource
   identified by the Request-URI. This method MAY be overridden by human
   intervention (or other means) on the origin server. The client cannot
   be guaranteed that the operation has been carried out, even if the
   status code returned from the origin server indicates that the action
   has been completed successfully. However, the server SHOULD NOT
   indicate success unless, at the time the response is given, it
   intends to delete the resource or move it to an inaccessible
   location.
</p>
<p>
   A successful response SHOULD be 200 (OK) if the response includes an
   entity describing the status, 202 (Accepted) if the action has not
   yet been enacted, or 204 (No Content) if the action has been enacted
   but the response does not include an entity.
</p>
<p>
   If the request passes through a cache and the Request-URI identifies
   one or more currently cached entities, those entries SHOULD be
   treated as stale. Responses to this method are not cacheable.
</p>
<h3><a name='sec9.8'>9.8</a> TRACE
</h3>
<p>
   The TRACE method is used to invoke a remote, application-layer loop-
   back of the request message. The final recipient of the request
   SHOULD reflect the message received back to the client as the
   entity-body of a 200 (OK) response. The final recipient is either the
</p>
<p>
   origin server or the first proxy or gateway to receive a Max-Forwards
   value of zero (0) in the request (see section 14.31). A TRACE request
   MUST NOT include an entity.
</p>
<p>
   TRACE allows the client to see what is being received at the other
   end of the request chain and use that data for testing or diagnostic
   information. The value of the Via header field (section <a rel='xref' href='rfc2616-sec14.html#sec14.45'>14.45</a>) is of
   particular interest, since it acts as a trace of the request chain.
   Use of the Max-Forwards header field allows the client to limit the
   length of the request chain, which is useful for testing a chain of
   proxies forwarding messages in an infinite loop.
</p>
<p>
   If the request is valid, the response SHOULD contain the entire
   request message in the entity-body, with a Content-Type of
   "message/http". Responses to this method MUST NOT be cached.
</p>
<h3><a name='sec9.9'>9.9</a> CONNECT
</h3>
<p>
   This specification reserves the method name CONNECT for use with a
   proxy that can dynamically switch to being a tunnel (e.g. SSL
   tunneling <a rel='bibref' href='rfc2616-sec17.html#bib44'>[44]</a>).
</p>
</body></html>
